Self-heating thermal interface material

ABSTRACT

A self-heating thermal interface material (TIM) may be formed using heating components dispersed within the TIM. The heating components may produce heat when the TIM is compressed. The heating components may be formed from microcapsules and the microcapsules may contain exothermic reactants. The reactants may be isolated from contact within the microcapsule until a compressive force is applied.

BACKGROUND

The present disclosure relates to the field of chemical compounds knownas thermal interface materials (TIMs). More particularly the inventionrelates to the application of a TIM in joining heat-sourcing devices toheat-dissipating devices in electronic or mechanical assemblies. Thethickness of the bond line of the TIM between the devices may affectthermal conductivity or other properties of the TIM. Higher compliancein a TIM can produce a thinner bond line, and heating a TIM can producea higher compliance in the TIM.

Multi-compartmental microcapsules are known in the art to be formed in avariety of structural configurations (e.g., concentric, pericentric,innercentric, or acentric) to form compartments within themicrocapsules. Compartments within a microcapsule may contain variouschemical elements or compounds.

SUMMARY

A self-heating Thermal Interface Material (TIM) increases thetemperature of a TIM during manufacture or repair of an electronic ormechanical assembly having one or more heat-sourcing andheat-dissipating devices joined at an interposing layer of the TIM.Aspects of the present disclosure describe a method for creating aself-heating TIM, a method for joining a heat-sourcing device with aheat-dissipating device including a self-heating TIM, and a self-heatingTIM.

Particular aspects of the disclosure relate to a method of creating aself-heating TIM by selecting a TIM having a particular compliance atambient temperatures and a higher compliance at an increasedtemperature. A TIM may be selected from a class of high performanceTIMs, including phase-change TIMs, silicone based TIMs, and acrylatebased TIMs (or, mixtures thereof). In an aspect of the disclosure theTIM may be a high performance TIM. The method includes forming heatingcomponents, determining a proportion of the TIM sufficient to heat theTIM to a temperature that produces the increased compliance, anddispersing heating components within the TIM. The heating components mayproduce heat when the TIM is subjected to a compressive force. Theheating components may be formed so as to not alter desirablecharacteristics or properties of the TIM, such as its durability,thermal conductivity, shear strength, cohesive or bond strength, orother such properties.

Other aspects of the disclosure relate to a method for joining aheat-sourcing device to a heat-dissipating device, by interposing alayer of self-heating TIM between the devices. A compressive forceapplied to the device transfers to the TIM. Heating components withinthe TIM respond to the compressive force to produce heat, and the heatincreases the compliance of the TIM.

In yet another aspect of the disclosure a self-heating TIM is comprisedof a TIM and one or more heating components dispersed within the TIM.The TIM may be a high performance TIM, including phase-change TIMs,silicone based TIMs, and acrylate based TIMs (or, mixtures thereof). Aheating component may contain compounds that react exothermically whenin contact with each other, the compounds may be structurally isolatedwithin the heating component, and application of a compressive force tothe TIM may establish contact between the compounds. A heating componentmay be formed from a multi-compartment microcapsule.

The above summary is not intended to describe each illustratedembodiment or every implementation of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included in the present application are incorporated into,and form part of, the specification. They illustrate embodiments of thepresent disclosure and, along with the description, serve to explain theprinciples of the disclosure. The drawings are only illustrative ofcertain embodiments and do not limit the disclosure.

FIG. 1A is a diagram illustrating a electronic circuit board having aplurality of devices and a device with a heat sink joined to a devicewith an interposing layer of a TIM.

FIG. 1B is a diagram illustrating a mechanical device having a heat sinkjoined to the device with an interposing layer of a TIM, according tovarious embodiments.

FIG. 2A illustrates a heat sink and electronic module with aninterposing layer of TIM at ambient temperatures, according to variousembodiments.

FIG. 2B illustrates a heat sink and electronic module with aninterposing layer of TIM at higher temperatures, according to variousembodiments.

FIG. 3A depicts a multi-compartmentalized microcapsule, according tovarious embodiments.

FIG. 3B depicts a multi-compartmentalized microcapsule having an innerbarrier to form compartments, according to various embodiments.

FIG. 4A illustrates a multi-compartmentalized microcapsule containingreactants and an inner microcapsule.

FIG. 4B illustrates a multi-compartmentalized microcapsule in which thecapsule wall of an inner microcapsule is ruptured.

FIG. 4C illustrates a multi-compartmentalized microcapsule in which afirst reactant is dispersed within a second reactant.

FIG. 4D illustrates a multi-compartmentalized microcapsule in whichreactants within the microcapsule have generated heat.

FIG. 5 depicts a self-heating TIM interspersed with exothermicmicrocapsules, according to various embodiments.

FIG. 6 is a flowchart showing an exemplary process for forming aself-heating TIM, according to various embodiments.

FIG. 7 is flowchart showing an exemplary process for joining aheat-sourcing device to a heat-dissipating device with an interposinglayer of a self-heating TIM, according to various embodiments.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. Rather, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to a self-heating ThermalInterface Material (TIM). More particular aspects relate to a method offorming a self-heating TIM having heating components dispersed withinthe TIM. Other aspects of the disclosure relate to a method of applyinga self-heating TIM between a heat-sourcing and heat-dissipating device,compressing the TIM to produce heat, and the increased temperatureincreasing the compliance of the TIM. Yet other aspects of thedisclosure relate to forming a heating component for a self-heating TIMusing multi-compartmentalized microcapsules.

Electronic devices—such as electronic circuit boards, electronicmodules, silicon dies, and other electronic component—may produceexcessive heat during normal operations. Mechanical devices also maygenerate excessive heat during normal operations, such as rotatingmechanical shafts producing heat from friction, pipes conducting heatedmaterial, or other applications of mechanical devices in which amechanical component creates or is subject to excessive temperatures.Dissipating heat from components that produce excessive heat(hereinafter, “heat-sourcing devices”) may require joining the componentwith a heat-dissipating device, commonly referred to as a “heat sink”,and generally made of materials highly conductive of heat and formed inshapes that increase heat-dissipating surfaces.

A TIM may be interposed between the heat-sourcing device and the heatsink to improve the efficiency of heat transfer from the heat-sourcingdevice to the heat sink. The thermal efficiency of a particular TIMderives from its intrinsic thermal conductivity. Certain classes of TIMsthat have particularly good thermal conductivity and other desirableproperties may be referred to as high performance TIMs. Properties of ahigh performance TIM may include the thermal conductivity of the TIM,the durability of the TIM, the shear strength of TIM, and/or the rangeof compliance of the TIM. For example, phase-change TIMs, silicone basedTIMs, and acrylate based TIMs may be considered high performance TIMs. Ahigh performance TIM may be formed as a mixture of various highperformance TIMs.

A bond line is a layer of TIM interposed between one or more surfacesjoining the devices. The thickness of the TIM bond line affects thermalconduction between the heat-sourcing device and the heat sink. A thickbond line reduces the efficiency of the TIM in transferring heat fromthe heat-sourcing device to the heat sink, and accordingly a thin bondline is desirable. During manufacture or repair of heat sourcingdevices, a heat sink is commonly joined to the heat-sourcing device atan interposing bond line of a TIM. The thickness of the bond line is inpart determined by the viscosity and corresponding compliance of theTIM. Compliance is a measure of the ability of the TIM to flow and TIMswith lower compliance produce thicker bond lines. Heating a TIM mayincrease its compliance and correspondingly produce a thinner TIM bondline.

Methods to heat a TIM may require heating an entire electronic ormechanical assembly containing the heat-sourcing device and heat sink,or to develop special devices or apparatus to direct heat to onlycomponents of an assembly having a heat-sourcing and heat sink device.To sufficiently increase the compliance a TIM to achieve a preferablythin bond line may require raising its temperature substantially, suchas by as much as 30 degrees Celsius. Heating an entire electronic ormechanical assembly can adversely affect or damage both theheat-sourcing and heat sink devices as well as other components of theassembly, and consequently may be impractical. Heating an entireassembly is also difficult or may not be possible during field repair ofan assembly in a customer installation. Developing special devices todirect heat to only a combination of heat sourcing and heat sink devicesis complex, time consuming, costly, and may be impractical according tothe design of an assembly of for field repair of an assembly. A methodof forming a self-heating TIM and a method of applying a self heatingTIM in joining heat sourcing and heat sink devices overcomes thesedisadvantages.

Accordingly, the present disclosure describes a self-heating TIM, amethod for creating the self-heating TIM, and a method for applying aself-heating TIM interposed between a heat sourcing device and a heatdissipation device.

FIG. 1A illustrates an electronic assembly 100 having a circuit board110, and a number of electronic components 101 a, 101 b, 101 c, and 104.Some components of an assembly—such as 101 a, 101 b, and 101 c—may notrequire application of a heat sink to dissipate heat in normaloperations. Other components, such as component 104, may generatesufficient heat during operations as to require a heat sink 102 todissipate the heat. For example, the component 104 may be an electroniccircuit module, a circuit chip, a circuit die, a power supply, or athermal plane within the circuit board 110 that may generate or conductexcessive heat during normal operations. Such components may require aheat sink, such as heat sink 102, to dissipate the excess heat.

A bond line 103 of a TIM may be interposed between the component 104 andthe heat sink 102. The TIM may be a high efficiency TIM that hasparticularly desirable thermal or other properties; for example,phase-change TIMs, silicone based TIMs, and acrylate based TIMs may behigh efficiency TIMs. A self-heating TIM may be made from a highefficiency TIM.

FIG. 1B depicts an application of a heat sink to a mechanical device.For example, an electric motor 124 may have a rotating shaft 125 and themotor 124 may produce excessive heat during normal operations. Theelectric motor 124 may require a heat sink 122 to dissipate the excessheat produced while operating and the heat sink 122 may be joined to theelectric motor 124 with an interposing layer of a TIM 123. In variousembodiments, the mechanical device may be any mechanical device orapparatus (e.g., a pipe) that, through friction or conduction of heatthrough its internal components or surfaces, may require a heat sink todissipate heat from the device.

FIG. 2A depicts an electronic component 200 and a heat sink 201 havingan interposing bond line of a TIM. For purposes of the disclosure, andwith respect to FIG. 2A and FIG. 2B, “TIM 202” refers generically to aTIM placed between an electronic component 200 and a heat sink 201. InFIG. 2A and FIG. 2B a particular instance of a TIM is referenced as TIM202 with a letter appended to it, such as TIM 202 a and TIM 202 b.

Temperatures typical of manufacture or field repair (hereinafter,“ambient temperatures”) may range between 25 (i.e., room ambient) and 35degrees C. At ambient temperatures of an electronic assembly a TIM 202may have a particular thickness T1 of a bond line, indicated as TIM 202a. The thickness T1 may be commensurate with the compliance of a TIM 202at an ambient temperature. For example, TIM 202 a may be a highperformance TIM, and at an ambient temperature the TIM 202 a may have abond line thickness T1 of more than 5.0 microns.

Increasing the temperature of a TIM 202 may increase the compliance ofthe TIM, and may produce a thinner bond line of the TIM 202. FIG. 2Billustrates TIM 202 a at an increased temperature (e.g. by 30 or moredegrees Celsius above room ambient), indicating Tim 202 a at anincreased temperature as TIM 202 b. The increased temperature mayincrease the compliance of the TIM and may produce a bond line of theTIM 202 b having thickness T2, and the bond line thickness may becommensurate with the increased compliance. For example, increasing thetemperature of the TIM 202 a by 30 or more degrees Celsius above roomambient may result in a thickness T2 of the bond line of TIM 202 b lessthan 2.0 microns.

Ambient temperature, ranges of temperatures, and thickness T1 and T2 ofthe TIM 202 bond line are disclosed for purposes of illustration andunderstanding of the disclosure, and are not meant to otherwise limitthe scope of embodiments of the invention.

Heating a TIM 202 may result from applying a compressive force to theTIM. In embodiments the compressive force may result from pressing theheat-dissipating structure 201 and the electronic component 200 togetherat the point of the interposing bond line. In some embodiments thecompressive force may be applied temporarily at the time of manufactureor field repair by mechanically pressing the heat sink 201 to thecomponent 200 manually or with a machine or tool adapted for manufactureof the electronic assembly. In other embodiments the compressive forcemay result from mechanically fastening the heat sink to the componentwith screws, springs, bolts, or other mechanical devices common in theart to mechanically fasten a heat sink to an electronic or mechanicalcomponent.

In various embodiments, the TIM 202 may be self-heating and the heat toproduce a thinner bond line, T2, may be produced by the compressing theTIM 202 in the manners described. In an embodiment the amount ofcompressive force applied to the TIM 202 may be determined by theprocess to manufacture or repair the electronic assembly or itscomponents without damaging the heat sink 201 or electronic component200. A self-heating TIM may be composed so as to produce heat at thetypical compressive load of that particular manufacture or repairprocess.

FIG. 3A illustrates a structure for a heating component according to themanner of the invention. A microcapsule 300 is a multi-compartmentalmicrocapsule illustrated in a cutaway view, according to embodiments.Microcapsule 300 has an outer wall 301 and contains an innermicrocapsule 302 and a first reactant 303. The inner microcapsule 302has a capsule wall 304 and contains a second reactant 305. The firstreactant 303 within the microcapsule 300 may surround the inner capsule302 and the first reactant 303 may be prevented from contacting thesecond reactant 303 by the capsule wall 304 of the inner microcapsule302.

The capsule wall 304 of the inner capsule 302 may be formed to ruptureunder a particular compressive force and the outer wall 301 of themicrocapsule 300 may be formed so as to not rupture under thatcompressive force. Rupturing the capsule wall 304 of the inner capsule302 may allow the second reactant 305 to contact the first reactant 303and the reactants may then chemically or physically react. In variousembodiments the reaction may be exothermic.

FIG. 3B illustrates an alternative microcapsule structure. Amicrocapsule 310 is a multi-compartmental microcapsule illustrated in acutaway view, according to embodiments. Microcapsule 310 has an outerwall 311 and contains a first reactant 313 and a second reactant 315. Amembrane 314 within the microcapsule 310 may prevent the first reactant313 and the second reactant 315 from coming into contact. The membrane314 may be any form of a physical barrier that forms two or morecompartments within the microcapsule 310.

The membrane 314 may be formed to rupture under a particular compressiveforce and the outer wall 311 of the microcapsule 310 may be formed so asto not rupture under that compressive force. Rupturing the membrane 314may allow the first reactant 313 to contact the second reactant 315 andthe reactants may then chemically or physically react. In variousembodiments the reaction may be exothermic.

In embodiments the compressive force applied to a self-heating TIM maybe within the range of that typical of that applied in the manufactureor repair of electronic assemblies or components having heat sinks, orin the manufacture or repair of mechanical assemblies or components thathave heat sinks. In embodiments the inner capsule wall 304 of amicrocapsule in the manner of microcapsule 300, or a membrane 314 of amicrocapsule in the manner of microcapsule 310, may rupture at a forceno greater than the lower bound of this range of compressive force. Anouter wall 301 or 311 of a microcapsule may sustain, without rupturing,a force no less than the upper bound of this range of compressive force.

Other embodiments may utilize more than two reactants. The microcapsule300 of FIG. 3A may contain a plurality of inner microcapsules, such as302, and the inner microcapsules may themselves contain other, inner,microcapsules. The various microcapsules may contain reactants and mayrupture under compression to allow the reactants to come into contact.Similarly, the microcapsule 310 of FIG. 3B may contain a plurality ofcompartments formed by a plurality of membranes or barriers, such as314, and that the compartments may in turn contain one or more membranesor barriers, or may contain microcapsules. The various membranes orbarriers may rupture under compression to allow the reactants to comeinto contact.

FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D illustrate configurations of amulti-compartmentalized microcapsule under a compressive force, and thecompression causing the reactants within the microcapsule to mix,according to various embodiments. FIG. 4A illustrates a firstmicrocapsule containing reactants and an inner microcapsule. FIG. 4Billustrates the first microcapsule of FIG. 4A in which the innermicrocapsule wall is ruptured. FIG. 4C illustrates the firstmicrocapsule of FIG. 4B in which a reactant contained in the innermicrocapsule is dispersed within a reactant initially surrounding theinner microcapsule. FIG. 4D illustrates the first microcapsule of FIG.4C in which the reactants have produced a reaction product within thefirst microcapsule and generated heat.

In more detail, FIG. 4A illustrates a microcapsule 400 formed similar tothe structure of the microcapsule 300 of FIG. 3A. Microcapsule 400 mayhave an outer wall 401 and may contain a first reactant 403 and an innercapsule 402 a. The inner capsule 402 a may have an outer capsule wall404 a and may contain a second reactant 405 a.

A compressive force may be applied to the microcapsule 400 a, which maycause the capsule wall 404 a of an inner microcapsule 402 a to rupture.FIG. 4B illustrates a configuration of microcapsule 400 in which thecapsule wall 404 b of the inner microcapsule 402 b may rupture undercompression of the microcapsule 400, indicated by the broken line of thecapsule wall 404 b. FIG. 4C illustrates the configuration ofmicrocapsule 400 in which the second reactant 405 c may become dispersedwithin the first reactant 403 c, in response to the inner microcapsule402 b having ruptured. The dispersion of the second reactant 405 cwithin the first reactant 403 c may cause them to react.

FIG. 4D illustrates a configuration of microcapsule 400 in which thereactants 403 c and 405 c may have come into contact and may havereacted. The microcapsule 400 may contain the product 405 d of thereaction of 403 c and 405 c and the microcapsule 400 may contain thereaction product 405 d so as to prevent the reaction product fromcontacting a material in which microcapsule 400 may be itself dispersed.The reactants 403 c and 405 c may have reacted exothermically to produceheat 416, and the heat may, as illustrated in FIG. 4D, transfer from themicrocapsule 400 to a material in which the microcapsule is dispersed.

In various embodiments, a self-heating TIM may utilize a microcapsulecontaining an oxidizing and a reducing agent to produce an exothermicreaction, such as oxygen and iron, respectively, according to thereaction equation:4Fe(s)+3O₂(g)===>2Fe₂O₃(s)Hrxn=−1.65103 Kj

According to the reaction equation 4 moles of iron react with 3 moles ofoxygen, such that in an embodiment iron may comprise 53% of the combinedmass of the two reactants and oxygen may comprise 43% of that combinedmass. In an additional embodiment, a microcapsule may contain ironpowder and hydrogen peroxide. The iron powder may be mixed with acatalyst such as ferric nitrate, which when in contact with the hydrogenperoxide liberates oxygen to react exothermically with the iron powder.For example, the microcapsule may use 1.5 moles of hydrogen peroxide permole of iron, for example 0.56 grams of iron powder to 0.51 grams ofhydrogen peroxide. The catalytic amount of ferric nitrate may be chosento achieve a desired reaction rate of heating, in Kilojoules per second.For example, between 0.001 and 0.005 gram equivalents of ferric nitrateper liter of hydrogen peroxide results in a reaction rate producing heatat between 100 and 500 Kilojoules per second.

With reference again to the microcapsule 300 of FIG. 3A, a microcapsulemay contain a mixture of iron powder and ferric nitrate in the innermicrocapsule 302 as the second reactant 305 and may contain hydrogenperoxide as the first reactant 303 surrounding the inner microcapsule302. Alternatively the inner microcapsule 302 may contain hydrogenperoxide as the first reactant 303 of the outer microcapsule may be amixture of iron and ferric nitrate as the second reactant 305. In someembodiments a microcapsule may have a diameter of less than 5.0 microns,or a microcapsule may have a smaller diameter of less than 2.0 microns.A ratio of 0.2 percent of such microcapsules per unit mass of the TIMmay produce a temperature increase of at least 1.04 degrees C. per gramof TIM, and may achieve a compliance value for a high efficiency TIMsthat results in a bond line as thin as 2.0 microns.

A structure similar to microcapsule 310 of FIG. 3B, including thevarious embodiments thereof, may operate similarly to the microcapsule400 of FIG. 4A through FIG. 4D to rupture the membrane 314, mix thereactants 303 and 305, and produce heat from an exothermic reaction 416of the reactants. It would be further apparent to one of ordinary skillin that art that an exothermic reaction may be produced by more than tworeactants, and that more than two reactants within a capsule may beisolated by more than one inner capsule or membrane, or more than one ofany other form of barrier isolating the reactants within the capsule. Avariety of reactants may be substituted to produce an exothermicreaction, or a variety of reaction rates and total heat produced,according to the manner of the invention.

FIG. 5 illustrates a cutaway view of a self-heating TIM 500 interposedbetween a heat sink 502 and an electrical device 503, such as aprocessor or ASIC module. The TIM 500 contacts the surfaces of the heatsink 502 at 501 a and the device 503 at 501 b, and may have a bond line(i.e., the mass of TIM 500 between surfaces 501 a and 501 b) thicknessT1 at ambient temperatures. The TIM 500 may have dispersed within it aplurality of heating components 505.

When the TIM is compressed between the heat sink 502 and device 503, theheating components 505 may initiate a reaction and the reaction mayproduce heat. The heat may be transferred to the TIM 500, and heatingthe TIM 500 may increase the compliance of the TIM 500. Increasing thecompliance of the TIM 500 may produce a bond line thickness of the TIM500 less than T1. In various embodiments, the heating components may bea structure similar to a microcapsule 300 or 310 as described inreference to FIG. 3A and FIG. 3B, respectively. Embodiments may disperseheating components, such as microcapsules 300 or 310, in a TIM 500, anda TIM 500 may be a high efficiency TIM including a phase-change TIM, asilicone based TIM, or an acrylate based TIM.

FIG. 6 exemplifies a method 600 to form a self-heating TIM, particularlyin an embodiment using a microcapsule according to one feature of theinvention. From a discussion of the method 600 it will be apparent toone of ordinary skill in the art the manner of modifying or adapting themethod to a variety of embodiments, including other embodiments of aheating component to disperse within a TIM. The method 600 should beunderstood to illustrate one manner of forming a self-heating TIM forpurposes of understanding the invention and should not be considered aslimiting the embodiments.

In method 600 at step 602 a TIM is chosen with consideration for theapplication of that TIM to a particular electronic or mechanicalassembly or the components thereof. In one embodiment, a TIM may bechosen for application in joining a heat sink to an electronic componentand a high efficiency TIM, such as previously disclosed herein, may beselected. In other embodiments, a TIM may be chosen for an applicationfor joining heat sinks to mechanical assemblies or components thereof.

At step 604 a desired thickness, or a desired range of thickness, of abond line of the TIM may be determined suitable for the application. Forexample, the desired thickness may be less than 5 microns or may be lessthan 2 microns. At step 604 a desired thickness may be determined inrelationship to a particular compliance, or range of compliance, valuesof the TIM, and a temperature of the TIM that may produce the compliancemay be determined.

At step 606 exothermic reactants compatible with the materials suitablefor forming a microcapsule may be chosen. The exothermic reactants maybe chosen to be inert with respect to the selected TIM, the material ofthe microcapsule walls, or an isolating barrier within a microcapsulewhen the reactants are not in contact. These may be chosen to be inertwith respect to the TIM or the outer microcapsule wall when thereactants are in contact, or such that the chemical products of thereaction are inert with respect to the TIM, outer microcapsule wall, andany remnants of the inner microcapsule wall or barrier.

At step 608 an amount of the first reactant and an amount of the secondreactant may be determined. The amounts may be determined from the totalamount of the reactants required to produce a desired amount of heat,the ratio of each reactant according to a reaction equation, the desireddimensions of the microcapsule, and the manner of isolating thereactants within the capsule. For example, a microcapsule may be desiredhaving a maximum dimension less than or equal to a desired finalthickness of a TIM bond line, such as less than 0.5 microns and theamount of reactants may be chosen corresponding to the volume availablewithin a microcapsule formed according to that dimension.

At step 610 one or more inner microcapsules, such as illustrated bymicrocapsule 302 of FIG. 3B, may be formed and the inner microcapsulesmay contain a first or a second reactant. In various embodiments, aninner microcapsule may be formed to contain a mixture of fine ironpowder and ferric nitrate, or may be formed to contain hydrogenperoxide. The inner microcapsule(s) may be formed with a capsule wallconfigured to rupture with application of a compressive force. The forcerequired to rupture an inner microcapsule wall may be determined fromwithin the range of compressive force typical of the manner of joiningor fastening a heat sink to a heat-sourcing device at a TIM bond line inthe manufacture or repair of the electronic or mechanical assemblies andcomponents thereof.

At step 612 an outer microcapsule may be formed containing the innermicrocapsule(s) and one or more other reactants, in the manner ofmicrocapsule 300 in FIG. 3A. The reactant(s) contained in the outermicrocapsule may be inert with respect to each other and themicrocapsule walls until in contact with one or more reactants containedin one or more inner microcapsules. In one embodiment an outermicrocapsule may contain hydrogen peroxide, or other oxidizers, whereone or more inner microcapsules contain finely powered iron and ferricnitrate, or other reductants. In another embodiment the outermicrocapsule may contain finely powered iron and ferric nitrate, orother reductants, where one or more inner microcapsules may containhydrogen peroxide or other oxidizers. The capsule wall of the outermicrocapsule may be formed to not rupture at the compressive force,determined in step 610, applied to rupture the capsule wall of the innermicrocapsule.

Alternatively, an embodiment may utilize a microcapsule having astructure as illustrated by microcapsule 310 in FIG. 3B. Step 608 may beomitted with respect to forming an inner microcapsule and, at step 610,an outer microcapsule may be formed having one or more membranes, in themanner of microcapsule 314 in FIG. 3B, forming two (or more)compartments within the outer microcapsule. The particular reactants maybe contained within the compartments, and the membrane(s) may be formedto rupture at compressive forces such as described in step 610 withrespect to the capsule wall of an inner microcapsule.

At step 614 a proportional amount of microcapsules may be determined tomix within the TIM. The determination may be made according to theamount of heat required to raise a particular amount of TIM from theambient temperature to the temperature required to produce the desiredcompliance of the TIM, considering also of the amount of heat producedby compressing a single microcapsule.

At step 616 an amount of TIM to apply to join a particular heat-sourcingdevice and a heat sink may be determined, and a corresponding amount ofmicrocapsules may be mixed into the TIM. For example, a TIM may be ahigh efficiency TIM and the TIM may achieve a desired compliance at atemperature of the TIM at least 31 degrees C. above room ambienttemperature. In the embodiment, utilizing the reactants and reactiondescribed in reference to FIG. 4A through FIG. 4D may require at least0.6 grams of the combined amounts of the reactants dispersed within 30grams of any of the preferred high efficiency TIMs.

FIG. 7 illustrates a method 700 for applying a self-heating TIM toreduce the thickness of the TIM bond line between a heat-sourcing (i.e.computer processor) and a heat-dissipating device (i.e., heat sink). Instep 702 a self-heating TIM may be selected. The selection may considerparticular properties of the TIM and of the assembly and heat-sourcingand heat-dissipating devices. The particular properties considered mayinclude the thermal conductivity of the TIM, the durability of the TIM,the shear strength of TIM, the chemical or physical suitability of theTIM with the heat-sourcing and heat sink devices, the compliance of theTIM at the ambient temperature, or the initial and desired finalthickness of the TIM bond line between the devices. In variousembodiments the heat-sourcing device may be an electronic component oran electronic assembly, or may be a mechanical device or mechanicalassembly. In an embodiment a TIM may be selected from a class of highefficiency TIMs and may consider properties particular to a TIMdesirable for that application. Other considerations may apply to aparticular assembly, devices, manufacturing process, or field repairprocess and will be evident to one of ordinary skill in the art.

At step 704 an amount of TIM may be determined that produces an initialbond line thickness between the heat-sourcing and heat-dissipatingdevices. The compliance of the TIM at the ambient temperature ofmanufacture or repair may determine the initial thickness of the TIM.For example, in an embodiment an initial thickness of a high performanceTIM may be 5.0 microns or more, and a final thickness of the bond lineafter heating the TIM may be desired to be less than 2.0 microns.

At step 706 a selected TIM may be applied in the initial bond linethickness of step 704 between the surfaces joining the heat sourcingdevice and the heat-dissipating device. At step 708 the devices may bejoined together at the bond line of the TIM and joining the devices maycompress the TIM. In some embodiments a heat-dissipating device may bemechanically fastened to a heat-sourcing device. For example, a heatsink may be joined to an electronic component utilizing fasteners suchas screws, bolts, or springs. In other embodiments, the devices may bejoined with an adhesive compound mixed with or a property of a TIM, andthe devices may be pressed together, until the adhesive may cure, at thebond line of the TIM and compress the TIM. Accordingly, the compressiveforce applied to the TIM may vary within a range typical of themanufacture of electronic or mechanical assemblies and their componentshaving heat-dissipating devices (e.g., heat sinks), or within a range ofmechanical pressure applied to join the heat-sourcing andheat-dissipating devices until the adhesive has cured or otherwise hadeffect to bond the devices.

At step 708 compressing the TIM may produce an exothermic reactionacting to heat the TIM, and the increased temperature of the TIM mayproduce a second compliance of the TIM, and the second compliance of theTIM may produce a desired final thickness of the TIM bond line. At 710the TIM, the heat-sourcing device, and the heat-dissipating devices maybe cooled to ambient temperature or to a temperature corresponding tonormal operations of the assembly or component.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A self-heating thermal interface material (TIM),the self-heating TIM comprising: a TIM; and at least one heat producingcomponent dispersed within the TIM, wherein the at least one heatproducing component further comprises: at least one first microcapsule,the at least one first microcapsule having an outer shell, the outershell forming a boundary between the TIM and contents of the at leastone first microcapsule, the outer shell configured to sustainapplication of a compressive force without rupturing; at least one firstreactant and an at least one second reactant contained within the outershell; and at least one isolating structure within the outer shell, theat least one isolating structure preventing the at least one firstreactant and the at least one second reactant from coming into contactwhen the compressive force is not applied, the at least one isolatingstructure configured to rupture when the compressive force is applied,the rupturing causing the at least one first reactant and the at leastone second reactant to come into contact, the contact producing anexothermic reaction, the heat from the exothermic reaction transferringto the TIM.
 2. The self-heating TIM of claim 1 wherein the TIM isselected from the group consisting of: a phase-change TIM; a siliconebased TIM; an acrylate based TIM; and a mixture including any of aphase-change TIM, a silicone based TIM, and an acrylate based TIM. 3.The self-heating TIM of claim 1 wherein the at least one isolatingstructure is at least one second microcapsule, the at least one firstmicrocapsule contains the at least one first reactant and the at leastone second microcapsule, and the at least one second microcapsulecontains the at least one second reactant.
 4. The self-heating TIM ofclaim 1 wherein the at least one first reactant is hydrogen peroxide andthe at least one second reactant includes iron and ferric nitrate. 5.The self-heating TIM of claim 1 wherein the at least one isolatingstructure is at least one membrane, the at least one membrane separatingtwo or more compartments of the first microcapsule, and wherein the atleast one first reactant is contained within a first compartment and theat least one second reactant is contained within a second compartment.6. The self-heating TIM of claim 1 wherein the at least one firstreactant and the at least one second reactant are inert with respect toone or more of the TIM, the microcapsule, and the isolating structure.7. The self-heating TIM of claim 1 wherein one or more of the TIM, themicrocapsule, and the isolating structure are inert with respect to oneor more products of the exothermic reaction.